Amines 19.1 Amines 19.2 Naming Amines 19.3 Physical Properties of Amines

Amines Amines are organic compounds in which one or more H in ammonia, NH3, is replaced with alkyl or aromatic groups. H H H | | | H—N—H CH3—N—H CH3—N—CH3 ammonia

Classification of Amines Amines are classified as primary, secondary, or tertiary. In a primary (1°) amine, one carbon group is bonded to the nitrogen atom. A secondary (2°) amine has two carbon groups. A tertiary (3°) amine has three carbon groups. H CH3 CH3 | | | CH3—N—H CH3—N—H CH3—N—CH3 1° 2° 3°

Models of Amines The three-dimensional models show the shapes of amine molecules with one or more alkyl groups bonded to the nitrogen atom.

Common Names of Amines Simple amines are named as amino alkanes or alkylamines. Two ways of naming: CH3—CH2—NH2 aminoethane or Ethylamine NH2 | CH3—CH2—CH3 2-aminopropane or 2-propanamine

IUPAC Names of Amines In the first way amino is put before the carbon chain. In the second way the –e in the alkane name of the longest chain is changed to –amine. The chain is numbered to locate the amine group and substituents. NH2 | CH3—CH2—NH2 CH3—CH—CH3 aminoethane 2-aminopropane Ethanamine 2-Propanamine

Naming Secondary and Tertiary Amines (Not assessed) Each alkyl groups bonded to the N atom is named as N-alkyl groups in front of the amine name for the longest chain. HN—CH3 | CH3—CH2—CH2—NH—CH3 CH3—CH—CH2—CH3 N-Methyl-1-propanamine N-Methyl-2-butanamine

Aromatic Amines (Not assessed) The amine of benzene is named aniline. Aniline 3-Chloroaniline N-Methylaniline

Boiling Points of Amines, Alcohols, and Alkanes The boiling points of amines are higher than alkanes, but lower than alcohols of similar mass.

Hydrogen Bonding for Amines The polar N-H bond provides hydrogen bonding in 1°and 2° amines, but not 3°. However, the N-H bonds in amines are not as polar as the O-H bonds in alcohols.

Hydrogen bonding Hydrogen bonds can form between the lone pair on the very electronegative nitrogen atom and the slightly positive hydrogen atom in another molecule.

Solubility in Water Amines with 1-5 carbon atoms are soluble in water. The N atom in amines forms hydrogen bonds with the polar O-H bond in water.

Amines are compounds based on an ammonia molecule (NH3), where one or more of the hydrogen atoms is replaced by a carbon chain. Thus R—NH2 is a primary amine, while R—NH—R’ is a secondary amine, and R—N(R’)—R’’ is a tertiary amine. You will only be asked to name primary amines. Note that 2-aminopropane, CH3—CH(NH2)—CH3, is a primary amine, yet the haloalkane from which it was made, CH3—CHCl—CH3, is a secondary haloalkane. Hydrogen bonding occurs in amines, but it is not as strong as the hydrogen bonding occurring in alcohols because the N—H bond is not as polar as the O—H bond. So amines have lower boiling points than the corresponding alcohols.

Low-mass amines are miscible in water.

Solubility in Water Amines with 1-5 carbon atoms are soluble in water. The N atom in amines forms hydrogen bonds with the polar O-H bond in water.

Like ammonia itself, amines are bases. Amines turn litmus paper blue. Amines are the only class of organic compounds you will meet this year which turn litmus blue. C3H7—NH2 + H2O C3H7—NH3+ + OH– Learn this equation.

The low-mass amines are gases or volatile liquids with a noticeably fishy smell. (Actually, it is dead fish which smell of amines as the proteins in their flesh break down.) Aminomethane & aminoethane are gasses at room temperature Aminopropane & aminobutane are volatile liquids with a fishy smell Heavier aminoalkanes are solids at room temperature

Reactions Like ammonia itself, amines react with inorganic acids to form ionic salts which are soluble in water and have no odour. C3H7—NH2 + HCl → C3H7—NH3+ Cl– propyl amine propyl ammonium chloride

A few drops of universal indicator solution are added to dilute hydrochloric acid.

Ethylamine is a gas, so this bottle contains a solution of ethylamine in alcohol.

Learn this equation and the product name. Ethylamine is added dropwise until no further colour change takes place. C2H5—NH2 + HCl → C2H5—NH3+ Cl– ethylamine ethyl ammonium chloride Learn this equation and the product name.

We added acid dropwise until the mixture was exactly neutral. Amines are bases which react with acids to form salts, just like inorganic bases do.

Complex ion formation Aminomethane and aminoethane can from complexes with transition metals

This pale blue ppt is copper hydroxide Also like ammonia, amines react with copper sulfate solution to form a royal blue complex. Cu2+ + 4C3H7NH2 → [Cu(C3H7NH2)4]2+

Reaction with Haloalkanes Primary aminoalkane react with primary haloalkanes to form secondary aminoalkanes CH3Cl + CH3NH2  CH3NHCH3 + HCl Chloromethane + aminoethane N-methyl aminoethane